The term “adhesive” generically describes a class of “sticky” materials. Adhesives and adhesive applicators owe their innovation to the industrial revolution, which resulted in an explosion of technical and scientific breakthroughs. The breakthroughs of the industrial revolution included the introduction of new materials and ingredients for use in formulating market-specific and industry-specific adhesives. In creating novel adhesives, companies have diligently considered desirable qualities such as adhesive flexibility, toughness, minimum curing or setting time, and temperature and chemical resistance. Today, the technology and science of adhesives and apparatuses for their application is the foundation for a multi-billion dollar industry with over seven hundred companies competing for market share. More importantly, these companies strive to create and introduce novel adhesives as well as apparatuses and method for the simple, efficient, inexpensive, and safe application of adhesives.
One of the most significant adhesive technical breakthroughs of the past century has been the introduction of pressure-sensitive thermoplastic adhesives. Thermoplastic adhesives have excellent adhering qualities; they can be softened by heating and firmed by cooling. These characteristics help thermoplastic adhesives produce waterproof, resilient, and long-lasting flexible bonds. Thermoplastic adhesives have what is known as a “plastic memory” meaning that each time a thermoplastic adhesive is heated, it can be molded into any desired form.
Thermoplastic adhesives have significant applications in today's industry. For example, in the preparation of mass mailings, marketers often desire to attach a card, such as a credit card or the like, to a carrier document so that a consumer can peel the card easily from the carrier document. One method of making such an attachment involves the use of a pressure-sensitive, thermoplastic adhesive. For example, by using a heating container to melt the thermoplastic adhesive and a metering pump to dispense it during the printing or collating process, a portion of thermoplastic adhesive can be metered onto the carrier document and a credit card pressed against it.
In addition to the uses for thermoplastic adhesives described above, industry is now finding additional uses for them. For example, thermoplastic adhesives are routinely used and applied as small bond points to eliminate the use of mechanical fasteners, such as staples, screws, rivets, clips, snaps, nails, and stitching. Thermoplastic adhesives are also extensively used in the packaging and manufacture of cartons, boxes, and corrugated boards, bags, envelopes, disposable products (diapers and other paper products), cigarettes, labels, and stamps. In fact, today's demand for thermoplastic adhesives extends to very broad fields of use.
Increasingly, industry demands thermoplastic adhesive application at on-site locations from simple-to-use, efficient, and safe dispensing apparatuses. In providing thermoplastic adhesives for application to a surface, the previously known embodiments have contemplated all of the following thermoplastic adhesive carrying media and application methods: hot-melt “glue-gun” as adhesive dispensers; adhesive segment-laden carrier release tape for “by hand” adhesive application; use of a plunger-like dispensing system in combination with adhesive segment-laden carrier release tape; use of a cardboard box applicator system for use in combination with adhesive segment-laden carrier release tape; an electric automated dispensing system for use with adhesive segment-laden carrier release tape, which is activated by the pressing of a palm-sized push button; a hand-held mechanical adhesive segment applicator apparatus with a mechanical hand-operated trigger for advancing an adhesive segment-laden carrier release tape contained therein, and a stand for holding such a hand-held mechanical adhesive segment applicator with a powered system for activating the mechanical trigger automatically as a work piece is brought in contact with the adhesive segment applicator to apply an adhesive segment thereto.
Using a “glue gun” device is an inefficient, difficult, and at times unsafe method of applying thermoplastic adhesives to a desired surface. First, the cost of using this equipment is relatively high. The apparatus and method are also inefficient consumers of both energy and glue. Specifically, the costs of the operation of such a dispenser (electrical usage, wasted glue from droppings) for only short periods of time outweigh any other potential advantages which may be realized. Safety is also an issue. Glue-gun devices are potentially unsafe because they include a heat source to heat a quantifiable supply of adhesive material to its melting point. A major drawback of using such an instrument is that the hot, molten thermoplastic adhesive can burn untrained users, and can also melt the substrate the user is applying the glue to. Finally, application of thermoplastic adhesives from a glue-gun does not enable the thermoplastic adhesive to withstand cold temperatures or to cool to a smooth surface, but instead will typically leave “spider webs” in the dried adhesive. In short, glue-gun applicators of the prior art are inefficient, difficult, and unsafe.
Many of the shortcomings of the glue-gun applicators of the prior art were overcome by U.S. Pat. No. 5,935,670 to Downs (the “'670 patent”), which patent is hereby incorporated herein by reference. The '670 patent discloses a method for presenting cold adhesive segments for application to a desired surface. The technology of the '670 patent focuses mainly on the manufacture of a clean, unaltered carrier release tape having first and second release surfaces with different coefficients of friction, and the application thereto of adhesive segments at periodic intervals. The adhesive segment-laden carrier release tape is then wound into a roll. This embodiment allows a user to apply the adhesive segments from the carrier release tape by hand.
Although the adhesive segment-laden carrier release tape taught in the '670 patent provides a highly innovative and commercially successful product, application of the adhesive segments from the release tape onto a work piece in an efficient manner remains a challenge. Specifically, the coiled adhesive segment-laden carrier release tape must be unrolled to present an adhesive segment for application. After the adhesive segment has been applied to the desired surface, the tape must be unrolled an additional distance to ready the next adhesive segment for application. Advancing the carrier release tape manually in this manner is time-consuming, and the “spent” carrier release tape must be either torn off and disposed of or left intact and in the way. Finally, dropping or unintentional uncoiling of the unused roll of adhesive segment-laden carrier release tape may also be a problem.
U.S. Pat. No. 6,319,442 to Downs (the “'442 patent”) which patent is hereby incorporated herein by reference, further evolves the previously known adhesive segment-laden carrier release tape of the '670 patent. Like the '670 patent, the '442 patent also contemplates a carrier release tape, which has first and second release surfaces with different coefficients of friction, and the application thereto of adhesive segments at periodic intervals. But, unlike the '670 patent, the '442 patent contemplates a thermoplastic adhesive carrier release tape having a transverse line of slits or perforations precut across its transverse width and between the adhesive segments. The precut tape of the '442 patent thus allows individual portions of the carrier release tape and associated thermoplastic adhesives to be removed from the roll for manual application to a desired surface. While such an embodiment remedies the '670 patent's problem of having a length of uncut spent carrier release tape, the carrier release tape of the '442 patent (as well as of the '670 patent) does not lend itself to use in combination with a more efficient dispenser for application of the adhesive segments.
While the '670 and '442 Patents focus primarily on the creation of adhesive segment-laden carrier release tape, they also contemplate the use of the adhesive segment-laden carrier release tape in combination with numerous dispenser apparatuses. First, a plunger-like applicator, as detailed within both the '670 and '442 patents, proves manageable, but is essentially a manually operated device for applying adhesive segments to a work piece from an adhesive segment-laden carrier release tape. Another previously known thermoplastic adhesive applicator is the so-called box applicator. The box applicator encases a roll of adhesive segment-laden carrier release tape as disclosed within the '670 and '442 patents. The carrier release tape is advanced from the box applicator by hand. Exposed adhesive segments must be pressed between the surface to be glued and the top of the cardboard box applicator to ensure adherence. This application process exposes unspent adhesive segments to dust and other debris, which may cause the adhesive segments to lose their adhesive tack and damage or soil the desired surface. Furthermore, the box applicator is an entirely manually operated device.
Not all previously known devices for applying thermoplastic adhesive from adhesive segment-laden carrier release tapes are entirely manual in operation. Previously known semi-automated methods dispose of the need to advance manually the carrier release tape. For example, the box applicator described above may be modified to include a motor for automatically advancing the adhesive segment-laden carrier release tape from the box either at a fixed rate, corresponding to the rate at which a worker may comfortably press a work piece against the adhesive segments as they are dispensed, or in response to the pressing of a push button to activate the motor to advance the adhesive segment-laden carrier release tape by a selected amount.
A more advanced mechanical adhesive segment applicator apparatus and method is described in U.S. patent application Ser. Nos. 10/360,395 and 10/360,457, filed on Feb. 8, 2003, and U.S. patent application Ser. No. 10/368,231, filed on Feb. 18, 2003, all of which are assigned to the assignee of the present application and the disclosures of which are incorporated herein by reference. These patent applications describe a hand held mechanical device for applying adhesive segments to a work piece from a carrier release tape having pressure-sensitive adhesive segments attached thereto. An indexing mechanism is provided on the carrier release tape to facilitate the dispensing of individual adhesive segments. The indexing mechanism consists of a plurality of patterned scores, cuts, or indentations located in the surface of the carrier release tape. The hand held adhesive segment applicator apparatus includes a mechanism for engaging the carrier release tape by the indexing mechanism to advance the tape to expose a new adhesive segment to be disposed therefrom each time a trigger mechanism on the applicator is manually actuated. The hand held adhesive segment applicator may be mounted on a stand that holds the applicator in a desired adjustable position. A pneumatic actuator may be provided to engage the trigger of the applicator to advance the carrier release tape to expose a new adhesive segment to be dispensed from the applicator automatically. The actuator may be activated by a trigger mechanism that is mounted near where the adhesive segment is dispensed from the applicator, to be engaged by a work piece as an adhesive segment is dispensed therefrom. Alternatively, the actuator may be activated by a hand or foot operated switch.
A limitation of previous systems and methods for applying thermoplastic adhesives to a work piece from an adhesive segment-laden carrier release tape is that operation of such systems and methods actually to apply the thermoplastic adhesive to a work piece is essentially manual. Even in systems that provide for the automatic or powered advancement of an adhesive segment-laden carrier release tape, the exposed adhesive segment must be applied to the work piece by either manually moving the applicator in contact with the work piece or manually moving the work piece in contact with the applicator. Such systems and methods for applying thermoplastic adhesives to work pieces from an adhesive segment-laden carrier release tape are thus not well suited to high speed high volume applications.
What is desired, therefore, is a system and method for the automatic application of thermoplastic adhesives to work pieces from an adhesive segment-laden carrier release tape for use in high-speed high-volume assembly line-like applications. Such an adhesive segment applicator should provide for assured automatic release of the adhesive segments from the carrier release tape onto a work piece. Such a system should also provide accurate indexing and advancement of the carrier release tape to ensure proper operation and positioning of the adhesive segment in the applicator device and on a work piece.